During this phase, the uterine lining is eliminated from the body via the vagina. The average length of a period is between three to seven days. Sanitary towels or tampons are used to absorb the menstrual flow. Sanitary towels and tampons need to be changed at least every four hours. The use of tampon has been associated with an increased risk of developing a rare illness called toxic shock syndrome.

Follicular Phase

The follicular phase spans the length of time between the first day of menstruation and the moment of ovulation. During this time, the pituitary gland releases follicle-stimulating hormone (FSH) which stimulates the ovary to produce around five to 20 follicles which bead on the surface. Each follicle contains an immature egg, but only one follicle will mature into an egg; this can occur at around day 10 of a 28-day cycle. The growth of the follicles stimulates the lining of the uterus (endometrium) to thicken in preparation for possible pregnancy.

Ovulation Phase

Ovulation means the release of a mature egg from the ovary. This usually occurs at mid-cycle, around ± 2 weeks before the onset of menstruation. During the follicular phase, the ripening follicle causes a rise in the level of the sex hormone oestrogen. The hypothalamus in the brain recognizes these rising levels and releases a chemical called gonadotropin-releasing hormone (GnRH) which prompts the pituitary gland to produce boosted levels of luteinising hormone and FSH. Ovulation is triggered within 2 days by the high levels of luteinising hormone. The egg is funnelled into the fallopian tube by waves of small projections. The life span of the egg is around 24 hours. If the egg does not meet a sperm within the eggs life span, it will die.

Luteal Phase

The Luteal Phase is a term that is used to describe the time period that is calculated from the day after ovulation and runs through the remainder of a monthly cycle. This phase usually lasts ± 2 weeks and is fairly consistent with a woman's cycle. The egg bursts from its follicle during ovulation. The ruptured follicle remains on the surface of the ovary for the next ± 2 weeks. Thereafter the follicle transforms into a structure known as the corpus luteum. This corpus luteum starts releasing the sex hormone progesterone along with small amounts of oestrogen. This progesterone and oestrogen maintain the thickened uterine lining, while waiting for the implantation of the fertilized egg.

The corpus luteum needs the presence of an implanted fertilized egg and its associated hormones to continue producing elevated levels of progesterone and maintain the thickened uterine lining. If pregnancy does not occur, the corpus luteum withers and dies, usually around day 22 in a 28-day cycle. The falling production of progesterone allows the womb to shed its delicate lining, resulting in menstruation. This process repeats itself every cycle.